Age-related changes in the twitch contractile properties of human
thenar motor units.
Doherty, Timothy J., William F. Brown.
Faculty of Kinesiology, The University of Western Ontario, London,
Ontario, Canada N6A 3K7, Neuromuscular Unit, Department of Neurology,
New England Medical Center and Tufts University, Boston MA, 02111
APStracts 3:0438A, 1996.
The purpose of this study was to examine the effects of aging on the
contractile and electrophysiological properties of human thenar motor
units (MUs). Percutaneous electrical stimulation of single motor
axons within the median nerve was used to isolate and examine the
twitch tensions, contractile speeds and surfaced-detected motor unit
action potential sizes (S-MUAPs) of 48 thenar MUs in 17 younger
subjects (25 - 53 yrs) and 44 thenar MUs in 9 older subjects (64 - 77
yrs). A wide range of twitch tensions, contractile speeds, and S-MUAP
sizes was observed in both age groups. However, older subjects had
significantly larger MU twitch tensions and slower MU twitch
contraction and one-half relaxation times. These changes were
accompanied by increased S-MUAP sizes. These findings suggest that
the human thenar MU pool undergoes significant age-related increase
in MU size and slowing of contractile speed. Such adaptation may help
to overcome previously reported age-related losses of thenar MUs.
Received 10 July 1995; accepted in final form 21 August 1996.
APS Manuscript Number A737-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996